The goal of this proposal is to characterize the cellular immune response in patients with either high or low susceptibility to S. mansoni infection. Specifically, we will determine whether lymphocytes from these subjects recognize parasite antigen extracts and fractionated and cloned S. mansoni antigens that could be involved in protective mechanisms. T cell clones to specific antigen fractions will be obtained to characterize the lymphokines and the antigens involved in immunoprotection.